This invention relates to an apparatus for detachably clamping a machine component onto a shaft, and more particularly to a nut apparatus for a shaft having a threaded portion where a high clamping force on a machine component is necessary.
Heavy duty mining equipment utilize machine components, such as large rotary cutter drums to break up earth formations, i.e., rocky soil, coal and other mineral deposits. These machine components are rotatably mounted on large diameter shafts and secured to the shaft by a large diameter nut threaded onto a threaded shank portion of the shaft. These machine components are subjected to tremendous loads and vibrations necessitating a high clamping force between the affected machine components and securing nut to prevent inadvertent loosening of the nut from the shaft. This clamping force may be as high as 1,000,000 lbf which would require a torque on an 8 inch diameter nut to equal 100,000 lb-ft.
It is old in the art to use a wrench to apply the requisite torque to a conventional nut to couple a part to a shaft. But often-times it is impractical to use torque wrenches for large diameter nuts because of limited space availability to reach the nut or because the work site does not provide proper environment to effect the requisite torque on the nut with a special force multiplying torque wrench. Additionally, conventional torquing devices are limited to applying torque to a nut of up to 11/2inch diameter. Generally, the torque necessary to achieve high clamping force for an 8 inch diameter nut will exceed the limits of practicality.
The prior art has provided hydraulic lock nuts or tensioning nuts wherein a pressure generating member is attached to the nut for the purpose of actuating a pressure pad to effect the necessary clamping force. These hydraulic lock nuts are prohibitively expensive for large diameter nuts, inconvenient to use in certain environments, and require additional equipment.
An alternative solution to this problem is a mechanical locking nut shown by Gepfert U.S. Pat. No. 3,618,994 and Steinbock U.S. Pat. No. 4,622,730. The Gepfert patent discloses an arbor nut having a body portion including a threaded main bore receivable on a threaded shank of an arbor, a first and second side face, and a plurality of threaded bores extending from the first to the second face. The arbor nut is advanced over the threaded shank portion of the arbor until it abuts against the tooling. Pads are recessed into the plurality of threaded bores and a plurality of jacking screws, each having a spherical bearing surface adapted to contact a complementary spherical bearing seat of the swivel pad, are disposed within the threaded bores. As the jacking screws are rotated into the threaded bores, the spherical bearing surface seats the pads against the tooling to impart a high clamping force to the tooling to firmly lock the nut in place. However, the Gepfert arbor nut does not provide a uniform clamping force, but instead, a compression-type clamping force that is concentrated at the contact point between the pad and the tooling. Further, the Gepfert invention requires: (1) special pads that are awkward to insert and may be misplaced in the threaded bores; and (2) expensive specialty screws with spherical surface ends to seat onto the special pads.
The Steinbock patent discloses a fastening apparatus that includes a flange ring adjacent an element to be fastened, a collar having a plurality of bored and tapped holes, and a plurality of jack bolts threaded into each tapped hole. The collar is rotated on a threaded shank portion of a structure and may contact or form a small gap between the collar and the flange which abuts the element to be secured. Jack bolts are then rotated until the end portions extend from the collar to contact the flange to provide the necessary clamping force to hold the machine element in place. By utilizing the jack bolts to act in a compression force against the flange, the Steinbock apparatus can deform the flange and possibly the machine element, and also fail to provide a uniform clamping force.
Various other types of fastening arrangements are shown in U.S. Pat. Nos. 4,010,669 (Kloren) and 4,416,575 (McCarthy).